The invention relates to a circuit for frame rate (field repetition frequency) conversion in a video signal reproduction device using a motion-adaptive method, having a motion detector for producing motion values of pixels by means of which a device for switching the field sequence with the frame rate being doubled can be actuated.
Circuits of this type are generally used for doubling the field repetition frequency of 50 or 60 Hz in television sets in order in this way to reduce the large-area flickering and to produce a picture which is smoother overall.
For frame rate conversion, a distinction is drawn between static methods on the one hand and motion-adaptive and/or motion-compensating methods on the other hand.
In a static method, the two fields A and B are duplicated and, as shown in FIG. 7, are reproduced either successively (AABB, FIG. 7a) or interleaved (ABAB, FIG. 7b). AABB reproduction has the disadvantage that, although very good motion representation is feasible, edge flickering cannot be reduced in this way, however. In comparison to this, it is possible using the ABAB raster sequence, which in practice means duplication of the frame, to reduce edge flickering in stationary pictures. However, this type of reproduction will not cope with moving pictures.
Furthermore, static methods as shown in FIG. 8 are known which operate with an AA*B*B raster sequence, with the A* and B* fields being calculated using linear or nonlinear methods. For example, the use of median filters is known for this purpose, using which the fields (A*)n and (B*)n are produced by interpolation of the fields An and Bn, and Bn and An+1, respectively.
Motion-adaptive and motion-compensating methods differ from static methods by using a motion detector and/or a motion estimator block. The appropriate field interleaving is illustrated in principle in FIG. 9. The motion detector block produces only information about the presence of motion in the picture, while the motion estimator block also determines information about the magnitude and direction of the motion. This information can be used in various ways to improve the frame rate conversion. For example, it is possible to switch between the two static methods mentioned above on a pixel or frame basis, depending on this information.
However, a disadvantage of all these methods is the fact that they are highly complex, particularly if motion-dependent switching between the various raster or field sequences and interpolation are intended to be carried out.